TMD is a widespread chronic pain condition. Successful psychosocial treatments for TMD have been developed, but the mechanisms by which these treatments achieve their effects are not well known. The goal of this project is to evaluate the possible mechanisms responsible for treatment gains in TMD treatment. Men and women (N=106) with complaints of chronic facial pain for at least 3 months' duration will be recruited from the University Dental Clinics and from the community via advertisements and randomly assigned to either a Standard Conservative Treatment (STD) employing an intraoral splint plus anti-inflammatory agents, or to a Standard Treatment + Cognitive-Behavioral Treatment Program (STD+CBT), that will include standard treatment but also focus on changing self-efficacy and decreasing catastrophization. Both treatments will entail 6 clinic visits. Dispositional and situational variables derived from a comprehensive model of pain coping will be measured before and after treatment. The situational variables, including coping responses, mood states, situational appraisals and self-efficacy, will be measured in an experience sampling paradigm four times daily using a hand-held computer. This will be done to minimize retrospective biases that may have hampered earlier studies of treatment process. Dependent variables will be self-report measures of distress, pain, and interference with activities, as well as blood plasma levels of cortisol and selected cytokines, measured at the end of the 6-week treatment period, and at follow-up points thereafter up to a 12-month follow-up. It is expected that the STD+CBT treatment will result in measurable changes in constructs such as self-efficacy and catastrophization, and that these changes will be related to improved outcomes compared to the STD controls. It is also expected that outcome differences between groups will be associated with changes in inflammatory mediators (cytokine levels). Finally, it is suggested that changes in situational treatment process variables will be associated with changes in cytokine levels. The results may indicate the true active mechanisms of successful TMD treatment, if these mechanisms can be successfully identified it would have important implications for the development of more effective treatment programs.